Method for operating a compressor

ABSTRACT

A method for operating a compressor, which supplies an internal combustion engine that is assigned to the compressor at its output end with air compressed to a boost pressure, in which the boost pressure is reducible by releasing the compressed air at least partially via a pressure release valve. The air released via the pressure release valve is used for driving a compressor wheel of the compressor.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of U.S. patentapplication Ser. No. 12/327,022, filed on Dec. 3, 2008, which claimspriority to German Patent Application No. 10 2007 060 218.0, filed onDec. 14, 2007, the contents of all of which are hereby incorporated byreference in their entireties.

FIELD OF THE INVENTION

The present invention relates to the operation of a compressor whichsupplies an internal combustion engine assigned to the compressor at itsoutput end, with air compressed to a boost pressure, in which the boostpressure is reducible by releasing the compressed air at least partiallyvia a pressure release valve.

The invention also relates to a compressor, particularly for an internalcombustion engine.

BACKGROUND INFORMATION

An operating method of the type mentioned at the outset and acorresponding compressor are known from German Patent Application No. DE10 2005 010 792. In that document, a pressure release valve configuredas a pop-off valve is used in order to rapidly reduce the boost pressureproduced by the compressor, by diverting the compressed air to alow-pressure side at the input to the compressor. A cyclic flow isgenerated thereby, among other things, through a bypass that includesthe pop-off valve, which connects the high-pressure side of thecompressor to its low-pressure side.

The usual method described using the pop-off valve makes possible arapid reduction in the boost pressure. However, the problem withpressure equalization across the pop-off valve is that, in the case of arapid load change of the internal combustion engine, for instance, fromfull load, at which a throttling device of the internal combustionengine is open all the way, to overrun, at which the throttling deviceis substantially closed, and subsequently renewed full load operation,the boost pressure on the output side of the compressor, that is,upstream of the throttling device, has to be generated anew. This bringsabout a delayed response of the internal combustion engine with respectto torque that is output as referred to the torque command of thedriver.

Therefore, other usual design approaches provide that, alternatively orin addition to the pop-off valve in the bypass, one should position asecond throttling device upstream of the compressor. At least in someoperating states, these measures could prevent the undesired transfer ofthe compressor into a pumping state or even the complete dropping off ofthe boost pressure at rapid load change, but they require acomparatively large constructive expenditure in the form of anadditional actuating mechanism and a correspondingly complex controller.

SUMMARY OF THE INVENTION

It is accordingly an object of the present invention to improve anoperating method and a compressor, of the type mentioned at the outset,to the extent that the response of the compressor, and with that also ofthe supplied internal combustion engine, is improved, particularlyduring a load change, without requiring an increased complexity in thedesign and the controller of the compressor at the same time.

This object is attained, according to the present invention, by drivinga compressor wheel of the compressor using the air discharged via apressure release valve. It is advantageously achieved thereby that theenergy of the released compressed air does not remain essentiallyun-utilized, as is the case with bypass systems having a pop-off valve,in which the released air is conveyed non-directionally into an intakemanifold upstream of the compressor. Rather, according to the presentinvention, the energy contained in the released compressed air isadvantageously used for maintaining the speed of the compressor wheeland of the running gear that is possibly connected to it, or at leastfor preventing an excessive dropoff in the speed. One particularadvantage of the principle according to the present invention is that,after a positive load change, a very rapid buildup of the boost pressureis possible because the compressor wheel at no time assumes a speed thatis substantially below its nominal speed.

The design approach according to the present invention is alsodistinguished by a particularly low construction expenditure and by acorrespondingly simple controller, because the air released by thepressure release valve, according to one variant of the presentinvention, by contrast to usual systems, is conveyed in a special manneronto the compressor wheel, and that is a directed manner, in order toimplement the principle according to the present invention. Inparticular, no additional actuators are required.

When there is a positive load change, the fast response of thecompressor and the internal combustion engine is able to be ensured bythe pressure release valve being closed rapidly when necessary. Abuildup of the boost pressure, that sets in in this context, takes placeparticularly rapidly, based on the compressor wheel maintaining a highspeed, according to the present invention.

In one advantageous specific embodiment of the operating methodaccording to the present invention, the released air is able to beconveyed directly onto the compressor wheel of the compressor, forexample, so as to drive it. It is also possible, according to thepresent invention, to convey the released air tangentially onto possiblyprovided guide blades of the compressor, in order to drive thecompressor wheel according to the present invention.

In another very advantageous specific embodiment of the operating methodaccording to the present invention, in which the compressor has assignedto it a turbine that is in rotary connection with the compressor wheelso as to drive the compressor wheel, the released air may advantageouslyeven be directly conveyed onto the turbine. This variant of theinvention is used, for instance, in compressors which are integratedinto exhaust gas turbochargers and are mounted on a common shaft withthe turbine.

A further increase in efficiency of the operating method, according tothe present invention, is given advantageously if the compressor isthrottled on the input side, while the boost pressure is released viathe pressure release valve, according to the present invention. Thethrottling on the input side of the compressor reduces the air mass flowwhich the compressor has to compress, so that the work saved thereby mayalso advantageously be used to increase the speed of the compressorwheel. This means that, by a throttling on the input side, thecompressor or an exhaust gas turbocharger that includes the compressoris operated at greater efficiency, whereby advantageously a subsequentbuildup of the boost pressure is also able to be achieved more rapidly,even after the end of a load interruption.

If the compressor is a component of an exhaust gas turbocharger, aseparate second turbine may also advantageously be provided in rotaryconnection with the remaining running gear of the exhaust gasturbocharger, which is used especially so as to be driven by the airreleased via the pressure release valve according to the presentinvention.

Because of the rapid response, the compressor according to the presentinvention is particularly suitable for supplying an internal combustionengine of a motor vehicle, but it may also be used in connection withother uses of compressed air.

Further advantages, features and details result from the followingdescription, in which different exemplary embodiments of the presentinvention are shown with reference to the drawings. In this context, thefeatures mentioned in the claims and the specification may be essentialto the present invention either alone or in any combination.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic representation of a compressor according to thepresent invention, together with an internal combustion engine that isto be supplied.

FIG. 2 shows a simplified flow chart of a specific embodiment of anoperating method according to the present invention.

DETAILED DESCRIPTION

FIG. 1 shows a simplified block diagram of an internal combustion engine1 which is used, for example, to drive a motor vehicle, that is notshown. Internal combustion engine 1 may be developed as an Otto engineor a diesel engine, and includes an engine block, not identified ingreater detail, having one or more cylinders to which air is suppliedvia intake manifold 1 a. In intake manifold 1 a there is a throttlevalve 1 b which controls an air mass flow supplied to the cylinders, ina known manner.

Combustion exhaust gases of internal combustion engine 1 are dischargedthrough exhaust gas pipe 1 c that is also shown in FIG. 1. The airsupplied to internal combustion engine 1 is indicated in FIG. 1 by arrow110, and the exhaust gases generated by internal combustion engine 1 areindicated in FIG. 1 by arrow 120.

Internal combustion engine 1, according to the present invention, has acompressor 5 that is assigned to it at its input side and that suppliesit with air 110 that is compressed to a boost pressure. For thispurpose, compressor 5 has a compressor wheel (not shown), which is usedfor the compression of air 100 supplied to it at the input side.

Compressor 5 may be driven, for instance, by its own drive (not shown),which in particular may be designed to be electrical. However,compressor 5 is preferably a component of an exhaust gas turbocharger,and driven by a turbine 55, which is in rotary connection with thecompressor wheel of compressor 5, for instance, by a common shaft 55 a.

Turbine 55 of the exhaust gas turbocharger is driven, by exhaust gases120 generated by internal combustion engine 1, in a known manner.Thereafter, the exhaust gases leave a turbine chamber (not shown) thatincludes turbine 55, as shown by arrow 130.

Pressure release valve 5 a is provided to be able to reduce rapidly theboost pressure which air 110 has, compressed by compressor 5, in intakemanifold 1 a. A quick reduction of the boost pressure is required, forinstance, when a negative abrupt change in load appears in internalcombustion engine 1, and throttle valve 1 b is closed, in order toreduce the torque output by internal combustion engine 1.

Air 110 a, 110 b released via pressure release valve 5 a, according tothe present invention, is used for driving the compressor wheel ofcompressor 5.

In a first, very advantageous variant of the present invention, it maybe provided, for example, that released air 110 a is conveyed directlyonto the compressor wheel of compressor 5, so that the compressor wheelis driven in a comparable manner to a cold-air turbine. In the process,the air jet of released air 110 a, based on the pressure differencebetween the boost pressure in intake manifold 1 a and a pressureprevailing at the input side of the compressor wheel, transfers a pulseto the compressor wheel which further accelerates the compressor wheel,or at least prevents the falling off of the compressor wheel's speed. Inthis way, the speed of the compressor wheel does not fall substantiallybelow a nominal speed, even in response to a reduction in the boostpressure in intake manifold 1 a, so that a renewed buildup of the boostpressure in intake manifold 1 a is very rapidly possible, according tothe present invention. Because of this, the response of internalcombustion engine 1 that is supplied with compressed air 110 bycompressor 5 is improved, particularly in dynamic operating situations,such as rapidly successive load changes.

According to yet another advantageous specific embodiment of theoperating method according to the present invention, released air 110 amay also be conveyed tangentially onto guide blades of compressor 5.

An alternative variant of the operating method according to the presentinvention provides that released air 110 b is not conveyed directly ontothe compressor wheel of compressor 5, but rather onto turbine 55, whichis in rotary connection with the compressor wheel, which is the case inthe usual exhaust gas turbochargers, for example.

Analogously to the first variant of the invention described above, whichis also able to be used in the case of separately provided compressors5, that is, without an assigned turbine 55, in the second variant of theoperating method according to the present invention, the releasedcompressed air 110 b is advantageously used for preventing a dropoff inthe speed of the compressor wheel. Released air 110 b is preferablyconveyed directly onto the guide blades of turbine 55, which otherwisehave only exhaust gas 120 applied to them. Because of the conveying ofreleased air 110 b, according to the present invention, the speed ofturbine 55 and the compressor wheel of compressor 5 increases, and afurther dropoff is prevented, especially in response to a load changethat goes along with the reduction in the boost pressure.

A disproportional increase in the gas pressure at the input to turbine55, that is possibly generated by the method according to the presentinvention, may be avoided, for instance, by a specific, coordinatedactivation of a so-called waste gate (not shown), which makes possible,in a known manner, a pressure reduction from exhaust gas pipe lc intoregions of the exhaust gas tract situated at the output end of turbine55. This ensures that, when the method according to the presentinvention is used, turbine 55 is also able to be always operated at anoptimum operating point.

All in all, the principle according to the present invention makespossible accelerating the running gear of an exhaust gas turbocharger ora compressor wheel of compressor 5, at load changes or loadinterruptions at simultaneous boost pressure decrease, or at leastkeeping them at a higher speed level than usual methods, which makespossible a better response of compressor 5, and with that, of internalcombustion engine 1.

It is also conceivable to combine the method variants described above.

In addition, an air mass flow 100 supplied to compressor 5 at its inputside may advantageously be throttled by suitable throttling means (notshown). This ensures that the energy obtained from compressed, releasedair 110 a, 110 b, according to the present invention, for acceleratingthe compressor wheel, does not additionally have to be used for thecompression of an unnecessarily big air mass flow 100 supplied on theinput side, but is rather used only for increasing the speed of thecompressor wheel.

As the throttling means, one may use, for instance, an iris diaphragm, athrottle valve and/or a throttle blade or a baffle plate, or the like.All in all, the throttling makes possible a shift in the operating pointof compressor 5 in the direction towards higher efficiencies and also anincrease in the volume flow of released, compressed air 110 a to thecompressor wheel. Because of operating at higher efficiencies, a fasterboost pressure buildup is achieved after a prior load interruption.During travel operation of a motor vehicle including internal combustionengine 1, this becomes noticeable by a more rapid torque buildup and aclearly shorter response by the internal combustion engine.

According to one additional very advantageous variant of the presentinvention, released, compressed air 110 b may be conveyed onto aseparate turbine 56 which, analogously to exhaust gas turbine 55 of anexhaust gas turbocharger, is in rotary connection to shaft 55 a, onwhich the compressor wheel of compressor 5 is also situated. Theseparate turbine 56 for applying released air 110 b, that is under boostpressure, may especially advantageously be situated in its own turbinehousing, and, in particular, does not have to be situated in the regionof exhaust gas tract 1 c, where comparatively high temperatures prevail.

FIG. 2 schematically shows a simplified flow chart of the operatingmethod according to the present invention. A first step 200 of theoperating method, according to the present invention, in this casesymbolizes a normal state of internal combustion engine 1, in whichinternal combustion engine 1 is supplied by compressor 5 with air 110that is under boost pressure.

According to the present invention, it is checked in step 210 whether aload change of internal combustion engine 1 is present, in such a waythat the boost pressure built up by compressor 5 in intake manifold 1 ashould be reduced as quickly as possible. If this is the case, themethod according to the present invention branches to subsequent workstep 220, in which pressure release valve 5 a is activated according tothe present invention, and the compressed air 110 a, 110 b herebyreleased, is used, in the manner described several times above, fordriving either the compressor wheel of compressor 5 directly, or turbine55 of exhaust gas turbocharger or the like.

If no load change is taking place, or no decrease in boost pressure isrequired, pressure release valve 5 a is not activated in step 230.

1. A method for operating a compressor, the method comprising: supplying an internal combustion engine, assigned to an output end of the compressor, with air compressed to a boost pressure, in which the boost pressure is reducible by releasing the compressed air at least partially via a pressure release valve; releasing air via the pressure release valve; and conveying the released air onto a compressor wheel for driving the compressor wheel of the compressor.
 2. The method as recited in claim 1, wherein the released air is conveyed directly onto the compressor wheel of the compressor.
 3. The method as recited in claim 1, wherein the released air is conveyed tangentially onto guide blades of the compressor.
 4. The method as recited in claim 1, wherein the released air is conveyed onto a first turbine that is in rotary connection with the compressor wheel, so as to drive the compressor wheel.
 5. The method as recited in claim 1, wherein the compressor is throttled at its input side.
 6. A compressor for supplying an internal combustion engine, assigned to an output end of the compressor, with air compressed to a boost pressure, in which a pressure release valve is situated in order to reduce the boost pressure by at least a partial release of the compressed air, comprising: a compressor arrangement conveying the air released via the pressure release valve onto at least one turbine that is in rotary connection to the compressor wheel, so as to drive the compressor wheel.
 7. The compressor as recited in claim 6, further comprising: wherein the at least one turbine includes a first turbine in rotary connection with the compressor wheel; and a second turbine in rotary connection to the compressor wheel and situated in a separate turbine housing from a turbine housing of the first turbine, wherein the compressor arrangement conveys the released air via the pressure release valve onto the second turbine so as to drive the compressor wheel.
 8. The compressor as recited in claim 6, further comprising: a throttling arrangement at an input side of the compressor arrangement for limiting an air mass flow supplied at the input side.
 9. An internal combustion engine, comprising: a compressor configured to supply the internal combustion engine, assigned to an output end of the compressor, with air compressed to a boost pressure, in which a pressure release valve is situated in order to reduce the boost pressure by at least a partial release of the compressed air; wherein the air released via the pressure release valve is conveyed onto at least one turbine that is in rotary connection to the compressor wheel so as to drive the compressor wheel.
 10. The internal combustion engine as recited in claim 9, wherein the at least one turbine includes a first turbine and a second turbine, and wherein the compressor includes the first turbine in rotary connection with a compressor wheel, and the second turbine in rotary connection to the compressor wheel.
 11. The internal combustion engine as recited in claim 9, wherein the compressor includes a throttling arrangement at an input side of the compressor arrangement for limiting an air mass flow supplied at the input side.
 12. The internal combustion engine as recited in claim 9, wherein the released air is conveyed directly onto the compressor wheel of the compressor, and wherein the compressor is throttled at its input side.
 13. The internal combustion engine as recited in claim 9, wherein the released air is conveyed tangentially onto guide blades of the compressor, and wherein the compressor is throttled at its input side.
 14. The method as recited in claim 1, wherein there is a first turbine in rotary connection with a compressor wheel and a second turbine in rotary connection to the compressor wheel, and wherein the air is released via the pressure release valve onto the second turbine.
 15. The method as recited in claim 1, wherein the released air is conveyed directly onto the compressor wheel of the compressor, and wherein the compressor is throttled at its input side.
 16. The method as recited in claim 1, wherein the released air is conveyed tangentially onto guide blades of the compressor, and wherein the compressor is throttled at its input side.
 17. The compressor as recited in claim 7, wherein the released air is conveyed directly onto the compressor wheel of the compressor, and wherein the compressor is throttled at its input side.
 18. The compressor as recited in claim 7, wherein the released air is conveyed tangentially onto guide blades of the compressor, and wherein the compressor is throttled at its input side. 